Anion-Exchange Membrane Fuel Cells: Dual-Site Mechanism of Oxygen Reduction Reaction in Alkaline Media on Cobalt-Polypyrrole Electrocatalysts

The oxygen reduction reaction (ORR) processes in alkaline media that occur on a family of electrocatalyst materials derived from a Co containing precursor and polypyrrole/C composite material (PPy/C) are investigated here. The effects of Co loading and heat treatment temperature on the CoPPy/C materials are revealed through Structural evaluations and electrochemical Studies. Principle component analysis (PCA), a multivariant analysis (MVA) technique, is used to establish structure-to-property correlations for the CoPPy/C materials. In all cases, pyrolysis leads to formation of a composite catalyst material, featuring Co nanoparticles coated with Co oxides and Co2+ species associated with N-C moieties that originate from the polypyrrole Structures. Based on these correlations, we are able to propose all ORR mechanism that Occurs on this Class of non-platinum based fuel cell cathode catalysts. The correlations suggest the presence of a dual site functionality where O-2 is initially reduced at a Co-2(+) containing N-C type site in a 2 e(-) process to form HO2-, an intermediate reaction product. Intermediate species (HO2-) call react further in the series type ORR mechanism at the decorating CoxOy/Co surface nanoparticle phase. The HO2- species can undergo either further electrochemical reduction to form OH species or chemical disprotonation to form OH- species and molecular O-2.